Distinct accumulative and adhesive phenotypes of Streptococcus gordonii are produced by reversible phase variation. S. gordonii are important microbial components of healthy plaque and contribute to plaque development by interactions with other potentially pathogenic oral bacteria. Understanding phase variation and the roles these two phenotypes play in the microbial ecology of the mouth, therefore, are important to our understanding of oral health. Phase variation occurs at frequencies of 10(-4) to 10(-3) in rich medium. The more accumulative phase variant (Spp+) has normal levels of glucosyltransferase (GTF) activity and produces cohesive insoluble glucans from sucrose in which greater than 90% of the viable bacteria accumulate on saliva-coated hydroxyapatite (SHA) surfaces. The more adhesive phenotype (Spp-) has less GTF activity, does not exhibit sucrose promoted accumulation, is excluded from insoluble polymer produced by Spp+ cells, but shows significantly enhanced adhesion to SHA surfaces. The results suggest that surface properties changes relevant to the recognition and binding to salivary components is coordinately regulated with the expression of the GTF gene and that phase variation has an important ecological function. Regulatory loci of gtf have been identified and one (gtfR) sequenced. We propose to address the questions: 1) To what extent does Spp phase variation change adhesive properties, is this reflected by increased adhesion to oral mucosal cells, on which S. gordonii are found, and to platelets (as a model of endocarditis) and does this involve a change in more than one adhesive activity? 2) Which bacterial surface components (cell surface proteins and antigens) change during phase variation and are these associated with adhesiveness? 3) How is phase variation of the adhesive phenotype regulated at the level of DNA, is the GTF regulatory gene gtfR involved and are gtf and adhesin genes coordinately regulated by interactions with other chromosomal loci? It is probable that phase variation and other properties related to the oral microbial ecology of S. gordonii and other bacteria are regulated by environmental factors. These studies will contribute information on these aspects of microbial behavior and their potential pathogenic roles.